TREATING BRACKISH WATER IN SANDOVAL COUNTY FEBRUARY 19, 2010
Project Background Sandoval County drilled two exploratory wells in 2007 in Rio Puerco Basin/SE portion of San Juan Basin Penetrated brackish water aquifer 3500 below ground surface. Brackish water under artesian pressure (over 150 psi) and 150 degrees Fahrenheit Well 6 production capacity approximately 600 gpm.
Project Purpose Sandoval County proposed to develop a wholesale water utility Provide water to the City of Rio Rancho (5 MGD) Provide water to sustain growth over next 40 years in the area No other sources of potable water in area
Water Chemistry Brackish water defined by concentration of total dissolved solids Fresh water <1000 mg/l Brackish water : 1000-10,000 mg/l Seawater: 30,000 mg/l Sandoval County TDS: 12,000 mg/l
Water Chemistry Constituents of Concern TDS -12,000 mg/l Hardness 1500 mg/l ( 100 mg/l for drinking water systems) acceptable Calcium- 450 mg/l High Alkalinity -1800 mg/l Bicarbonate- 1800 mg/l
Water Chemistry Arsenic 635 ppb ( over sixty times MCL) Radium- 80 mg/l (sixteen times higher than MCL) Boron -9.7 mg/l (nearly twice as high as that found in seawater (5 mg/l) Carbon dioxide gas -1900 mg/l
Treatment Challenges CO 2 and H 2 S Arsenic and radionuclides Hardness (calcium and magnesium) Alkalinity Boron High temperature
Treatment Processes Aeration to remove CO 2 and H 2 S Coagulation/sedimentation to remove arsenic and radium Warm lime softening to reduce hardness and alkalinity Granular filtration to remove solids Ion exchange to remove remaining hardness Reverse osmosis to remove TDS and boron Cooling towers to reduce temperature
Treatment Goals Produce 5 MG of potable water meeting EPA Drinking Water Standards Reduce TDS to <500mg/L Reduce arsenic to < 8 ppb Reduce hardness to 100 mg/l Reduce radium to < 16 pci/l Selective recovery of treatment by-products Sodium chloride (NaCl)
Bench Scale Testing Conducted in June 2009 Determine pre-treatment processes Focus on hardness, alkalinity, TDS, and removal of arsenic and radium Determine dosages of pre-treatment chemicals Estimate chemical usage and volume of treatment system waste products
Pre-Treatment Process Train
Pilot Testing Conducted September November 2009 Evaluated pre-treatment processes and RO system Generate water quality projections for product and waste streams Establish design criteria and operating conditions for full-scale plant
Pilot Testing Parameters Caustic soda used in softening process instead of lime Coagulation and softening occur in same contact clarifier WAC ion exchange to remove remaining hardness and divalent ions High Efficiency Reverse Osmosis process using both brackish water and seawater membranes (4 stage process) 80% recovery target for RO process
Pilot Testing Process Flow Diagram
Pilot Testing Trailer and Equipment
Pilot Testing Trailer and Equipment
Pilot Testing RO Process
Pilot Testing Clarifier/Softening Process
Pilot Testing Clarifier/Softening Process
Pilot Testing Holding Pond
Pilot Test Results Pretreatment Processes Pretreatment processes successful Hydrogen sulfide and CO 2 reduced in aeration Arsenic and radionuclide reduced in coagulation/sedimentation Significant hardness removal in warm lime softening process Effective radionuclide removal in softening and granular filtration processes Ion exchange effective in reducing remaining hardness
Pilot Test Results RO Process RO Process Successful Achieved 80 percent recovery TDS reduced to < 200 mg/l Boron removal from 9.7 mg/l to 3 mg/l Concentrate contained primarily sodium chlorides and sodium sulfates Permeate requires stabilization to reduce corrosiveness of water Cooling required before introduction into system
Conclusions Brackish water supply can be treated to meet EPA Drinking Water Standards Significant pre-treatment required before RO process Significant challenges with disposal of waste products Possibility of beneficial recovery of byproducts, namely sodium chloride
Conclusions Estimated construction cost of full scale 5 MGD plant -$62.4 million Estimated annual O&M - $15.2 million ($6.75/100 gallons) Funding challenges
Questions and Comments